Japanese Patent Application Publication No. JP-A-2002-225578 describes a drive system incorporated in a vehicle where power is output from a motor to a drive shaft, which is connected to an axle, via a transmission. The system makes the power from the motor appropriate for the vehicle speed by changing the shift speed of the transmission in accordance with the vehicle speed, and then outputs that power to the drive shaft.
With this kind of drive system, in order to correct any deviations that may have occurred due to changes over time in the transmission and more appropriately change the transmission ratio of the transmission, it is desirable to perform a learning operation and control an actuator of the transmission using the learned results when the transmission ratio of the transmission is changed. In this case, it is desirable to perform the learning operation when the shift speed of the transmission is changed while the drive system is operating steadily. However, it is difficult to determine whether the drive system is operating steadily using the torque that is output from the motor, for example, when the shift speed of the transmission is changed while maintaining power output from the motor, because the torque that is output from the motor changes when the shift speed changes. Furthermore, in a power output device that outputs both power from an engine and power from a motor via a transmission to a drive shaft, it is difficult to determine whether it is operating steadily using torque that is output from the motor because the torque changes in response to a change in the power from the motor when the ratio between the power from the engine and the power from the motor is changed, even when it is operating steadily.